The present invention relates generally to the extraction of chitin from the exoskeletons of any exoskeletal animal. More specifically, it refers to the extraction of chitin from the exoskeletons of marine crustaceans, such as crab, shrimp, crayfish, and lobster. More specifically, the present invention relates to a primarily physical process of efficiently extracting chitin from exoskeletons, which is economical in its energy requirements, and substantially minimizes the use of harsh chemicals and the associated risks of their subsequent residues.
Shellfish, especially shrimp, is an increasingly popular food category in the western world. In 1998, for example, more than 1.5 billion pounds of crustaceans were consumed in the U.S. alone (U.S. Census Bureau, xe2x80x9cStatistical Abstract of the United States: 2000xe2x80x9d, Table #1160). One of the ever-more popular forms of this class of food is the meat removed from the shell, either raw or cooked. For example, the flesh of crab, crayfish, and lobster, which has been xe2x80x9cpickedxe2x80x9d from the shells, is an increasingly popular commercial category of seafood. However, a major consequence of this growing trend is that the shells, which are de-fleshed at central locations, pose a growing and potentially harmful waste-disposal problem.
It has been estimated that approximately 3.2 million metric tons of crustacean shells were produced by processing plants, worldwide, in 1999. This poses not only environmental and health hazards, but it is also a significant waste of the value represented by the chitin contained in all wasted shell material.
Chitin is a naturally occurring polymer that has great commercial utility and significant economic value. For example, chitin has been found to be particularly useful for the production of chitosan, which is useful in the treatment of municipal water, and as a raw material for the production of glucosamine, which is the nutritively important monomer of chitin.
Evident of the usefulness of natural chitin, there are currently many known methods of extracting the natural chitin from the exoskeletons of marine crustaceans. References illustrative of the prior art methods of separating, extracting and purifying the chitin from shellfish wastes include:
Chang and Tsai, 1997, xe2x80x9cResponse Surface Optimization and Kinetics of Isolating Chitin from Pink Shrimp Shell Wastexe2x80x9d, J. Agric. Food Chem., Vol. 45, pgs 1900-1904;
Kawaguti, ""62, xe2x80x9cElectron Microscopy of the Integumental Structure and its Calcification during Molting in a Crayfishxe2x80x9d, Biol. J. Okayama, Univ., Vol. 8, pp. 43-58;
No and Myers, 1995, xe2x80x9cPreparation and Characterization of Chitin and Chitosanxe2x80x94A Review, J. Aquatic Food Product Technol. Vol. 4, #2, pp 27-41;
Roer and Dillamen, 1984, xe2x80x9cThe Structure and Calcification of the Crustacean Cuticlexe2x80x9d, Amer. Zool., Vol. 24, pp 893-909;
Waterman, T. H. ""60, xe2x80x9cMetabolism and Growthxe2x80x9d, Vol. 1 in xe2x80x9cThe Physiology of Crustaceaxe2x80x9d, Acad. Press, p. 449, as cited in U.S. Pat. No. 4,199,496, Col. 3.
U.S. Pat. Nos. 4,066,735, 4,199,496, 4,293,098, 5,053,113, 5,210,186;
Japan Patent No. 5,310,804; and
WO Patent No. 8,606,082.
In general, the shells of exoskeleton animals, such as shrimp, have been reported to consist of a matrix of chitin, to which protein is covalently bonded (Chang and Tsai, 1997). This chitin/protein complex is reported to be xe2x80x98filledxe2x80x99 with unwanted fine granules of calcium carbonate (e.g. Roer and Dillamen, 1984, and U.S. Pat. No. 4,199,496). The extent of xe2x80x98fillingxe2x80x99 appears to be characteristic for each crustacean species and thus varies. Furthermore, there is also a variable amount of unwanted lipids associated with these exoskeleton matrices, and these lipids are primarily in the form of a lipo-protein membrane, especially the epicuticle (Roer and Dillamen, 1984).
As such, to be functionally useful, the chitin must be effectively separated from these unwanted non-chitinous materials, specifically the lipids, protein, and calcium carbonate. However, since chitin is insoluble in virtually everything except highly concentrated acidic solutions, the conventional practice is to remove the unwanted non-chitinous contaminants from the insoluble chitin matrix by using strong, and environmentally hazardous, acidic solutions.
Prior art efforts to accomplish this separation have utilized chemicals and chemical procedures including boiling lye (U.S. Pat. No. 5,210,186); alkali with constant electrical current (U.S. Pat. No. 5,053,113); sulphurous acid (U.S. Pat. No. 4,066,735); sodium hydroxide, followed by hydrochloric acid (No and Myers, 1995; see also U.S. Pat. No. 4,199,496); de-mineralization by acid, followed by de-proteination by enzymic activity of fish viscera (WO Patent No. 8,606,082); and de-mineralization by acid and de-proteination by soap (Japan Patent No. 5,310,804).
However, such chemicals and solutions are not only costly, but they also present extreme occupational hazards for workers and create environmental dangers due to subsequent handling and waste disposal. Furthermore, regardless of the separation means used to remove these unwanted contaminants from the natural chitin, residues of these harmful chemicals and solutions will remain in the final chitin product, wherein a majority of these chemical residues are believed to be hazardous to human and animal health. As such, the residual chemical presence is at odds with the main purpose of final chitin usages, which include promoting human health. The present invention overcomes these limitations by drastically reducing the reliance and need to use harmful chemicals and/or solutions to remove unwanted chitin contamination. As such, with the present invention, due to the fact that little or no chemical solutions are required, residual chemical presence in the final chitin product is kept to a minimum, thus increasing the healthful usefulness of the end chitin product.
The recovery of chitin from shellfish exoskeletons without chemicals was first disclosed by U.S. Pat. No. 4,293,098 (""098), issued to Muralidhara, using the purely mechanical steps of drying, grinding, and air classification. However, a limitation of the ""098 patent is that the requirement of drying the whole shell offal is very demanding of energy, and therefore costly and inefficient. Also, when dried, the chitin matrix becomes lithified to the point that it can best be described as vitreous in nature, and thus much more difficult to cut or grind. Furthermore, it is apparent that when dried ab initio, the protein and lipid contaminants become bound to the chitin, and to each other, making them much more resistant to subsequent separation. This binding of protein and lipid to the chitin is most often described as being chemical in nature (e.g. No and Meyers, 1995, p. 37). Research has been formed and it is most likely a case of tenacious adhesion, as when a dirty cooking pot is allowed to become dry before washing. Whatever the cause, the result is the same: drying the whole shell offal makes the subsequent removal of non-chitinous materials very difficult and inefficient. Pre-drying in this manner, particularly if done, for example, with a rotary kiln or the like, is further likely to result in the production of undesirable thermal decomposition by-products, particularly the protein and lipid, which will need to be eliminated later at considerable cost.
Furthermore, the ""098 patent fails to specify how much undesirable residual lipid and calcium remain in the product after final air classification to separate and extract the desired chitin product. In practice, it has been found that this practice of drying the whole offal in fact makes the desired chitin size-reduction and separation much more difficult, and thus more complicated and expensive. Furthermore, it has been observed that the drying of whole shell offal is impractical to conduct on-site at individual peeling or picking facilities, due to energy and machinery requirements, and therefore considerations of economy and efficiency necessitate that this offal be accumulated and stored until it is efficient to transport it to a central drying facility. This required storage increases the cost of the process, and leaves the waste material vulnerable to deterioration and contamination by insects, rodents, birds, and bacteria. All such contamination either reduces the quality of the chitin extracted, and/or increases its cost by requiring eventual clean-up. The present invention overcomes these limitations by negating the need for a drying phase prior to cutting the chitin. Furthermore, the preferred embodiment of the present invention is intended to be conducted on a small scale, whereby having minimal energy and machinery requirements, and where the process can occur at individual peeling or picking facilities, thus negating the requirement that the whole shell offals are kept in a holding container, wherein susceptible to contamination.
It is therefore an object of the present invention to provide an improved and more economical method of separating and extracting chitin from shellfish exoskeletons without the need for harmful and dangerous chemicals and solutions.
It is a further objective of the present invention to provide a method for extracting chitin that is essentially free of objectionable chemical residues and is more suitable for the use in producing safe and healthy food and medical products.
It is still a further object of the present invention to provide a chitin extraction process that has no chemical exposure risk for workers, and no chemical residuals that could pose a disposal and handling risk to the environment.
It is yet another object of the present invention to provide a means of extracting chitin which avoids the necessity of drying the shellfish offal in its whole shell form.
Numerous other objects, features, and advantages of the present invention will become more readily apparent through the following detailed description of the preferred embodiment of the present invention, drawings and the claims.
The present invention is a physical method of efficiently extracting chitin from the exoskeletons of marine crustaceans. The present invention preferably cuts the chitin-rich exoskeletons while the exoskeletons are in a wet state. It is within this wet state that the exoskeletons are apparently softer and have a decreased chance of unwantedly wearing the cutting surfaces. As well, the shells have a reduced chance of fracturing, thereby yielding a more controllable cutting process. Upon cutting the exoskeletons into a predetermined particle size, the exoskeleton particles are then diluted, preferably in a water-based solution, which enhances the exoskeleton""s pumping capabilities, as well as provides for a means of washing the cut exoskeletal material.
The diluted and washed particles are then filtered, thus separating the larger (mostly chitinous) particles from the smaller (mostly non-chitinous) particles and water. The exoskeleton material is once again reduced in particle size even further, diluted and mixed, preferably with a water solution, and finally separated again using a filtering means. The final exoskeletal residue is fully washed and subsequently has an approximate chitin concentration of up to 65%, as well as an almost complete reduction of lipids and protein and minimal calcium contamination.